Automobile scrap is used in many foundries as a source of iron for cast iron. With the increasing use of aluminum in automobiles, the aluminum level in the automobile scrap is significantly higher than in years past. Moreover, it has been found that the addition of aluminum to a coupla charge may reduce coke consumption and silicon loss as well as increase the melt temperature and reduce the sulfur content of the molten cast iron produced therefrom This iron contains higher then normal and deleterious amounts of aluminum. Regardless of the source of aluminum, the aluminum level in molten cast iron may easily reach a level where harmful effects are experienced. For example, the literature indicates that aluminum concentrations greater than 0.01% by weight may cause pinholes in the castings In addition to the pinholes, the presence of aluminum causes excess dross formation due to continuous oxidation of aluminum to aluminum oxide which all too often becomes entrapped in the melt which, in turn, introduces inclusions in the castings. Moreover, excess dross formation creates metal handling problems and increases the metal loss.
Heretofore, attempts have been made to oxidize the aluminum by bubbling air and/or oxygen through the melt or by using a high velocity lance positioned above the melt surface and projecting the oxygen/air onto the surface. Moreover, solid reagents such as iron ore, ferric oxide, sodium sulfate, or manganese oxide have also been used to oxidize the aluminum. Unfortunately, such oxidizing agents also react with any carbon and silicon present in the melt and thereby reduce their concentrations. The sodium sulfate additionally contaminates the melt with sulfur and produces sodium vapor. Chlorine and molten manganese chloride flux have also been reported as candidates for removing aluminum without affecting the silicon and carbon content of the melt. Chlorine unfortunately produces a considerable amount of iron chloride fume which causes a pollution problem. Dolomitic limestone addition has also been proposed, but this results in oxidation of carbon, adsorption of heat from the melt incident to the decomposition of the carbonates, and formation of considerable MgO and CaO dust aggravated by the formation of CO.sub.2 gas. Finally, manganese metal containing nitrogen has been proposed, but is ineffective to reduce the aluminum content to below 0.01%.
It would be desirable to develop a simple, inexpensive pollution-free process of dealuminizing molten cast iron without scavenging the carbon and/or silicon from the molten metal.
Accordingly, it is an object of the present invention to provide a process for dealuminizing molten cast iron which process utilizes a molten SiO.sub.2 -based flux which, upon mixing with the molten iron, oxidizes the aluminum and any other metallic contaminants therein susceptible to silica oxidation (e.g., cerium) and advantageously seeds the molten iron with silicon without substantially depleting the iron of carbon or other desirable ingredients. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.